Downloading Steam Workshop mods without owning the game on Steam is possible for many titles , a command-line tool provided by Valve
steamcmd.exe (Windows) or ./steamcmd.sh (Linux/Mac).Steam> prompt, type:
login anonymous
Getting the .pak, .zip, or folder is only half the battle. Now you need to install it for the version of the game you actually own (GOG, Epic, etc.).
.zip or .rar file.workshop_download_item <App ID> <Mod ID>
The Official Way: You Can't
App ID: The number following /app/ (this identifies the game).